Apparatus such as aircraft engines, turbines, and pumps typically include at least one shaft that normally rotates at a relatively high speed. An apparatus such as an aircraft jet engine may include multiple shafts that normally operate at high speeds while passing through several zones of varying pressures. A jet engine creates thrust by compressing atmospheric air, mixing fuel with the compressed air and igniting it, and passing the ignited and expanded air/fuel mixture through a turbine. Zones having various pressures exist throughout the length of the engine. These zones must be sealed from one another in order to generally allow the engine to operate and in particular to increase the efficency of the aircraft engie. In addition to the high rotational speeds of an aircraft engine shaft, axial and radial shaft movement increases the difficulties associated with manitaining effective seals throughout the lifetime of the engine. An effective seal must be able to continuously accommodate both axial and radial shaft movement while maintaining the seal. When rigid seals are installed, shaft movement eventually creates excessive wear leading to an ineffective seal.
One type of seal that has been increasingly used in recent years in order to accommodate the shaft movement mentioned above is a brush seal. Numerous configurations of brush seals for use with shafts are known in the art. Each brush seal generally includes a ring-shaped body member having bristles extending therefrom. The bristles may extend radially inward or radially outward from the body portion. In a typical configuration, the bristles contact the rotating member while the body member is fixed to a stationary support member. The bristles are flexible enough to allow the shaft to rotate against it, and to move both axially and radially, while effectively maintaining a seal. The bristles may be constructed from a variety of materials. One common construction is the use of a plurality of metal or ceramic bristles that are held by the holding body member at one end and are free and contacting the moving shaft at the other end. Another construction includes a series of interlocking fingers.
In the past, brush seals have been used unsuccessfilly in apparatus such as aircraft engines, turbines, and pumps because of the high shaft speeds required by these devices. The high shaft speeds often cause the bristle portion contacting the shaft to rapidly deteriorate due to the amount of heat that is quickly generated at the shaft/brush interface and the shaft eccentricity. When the bristle portions are constructed from a stronger material (e.g., ceramics), the section of the shaft contacting the bristle portion undesirably wears causing the entire shaft to require replacement or rehabilitation. The frictional engagement of the brush with the rotating member also creates the undesirable generation of heat.